Update outdated PlaybackState enums in QML

With the refractor in f91e9f8, an abstraction over QtMultiMedia was
implemented. New enums for the PlaybackState were created, to not make
the application depend on QtMultiMedia. However, not all code was
updated to make proper use of these new enums.

This in turn caused the screen turned off while playing a video and the
HUD not showing when the video started buffering. This commit fixes
that.

Closes #51

sailfish/qml/components/videoplayer/VideoHud.qml

@@ -152,15 +152,10 @@ Item {
     Connections {
         target: manager
         onMediaStatusChanged: {
-            console.log("New mediaPlayer status: " + manager.mediaStatus)
-            switch(manager.mediaStatus) {
-            case J.MediaStatus.Loaded:
-            case J.MediaStatus.Buffering:
-                show(false)
-                break;
-            case J.MediaStatus.Buffered:
+            if (manager.mediaStatus == J.MediaStatus.Loaded || manager.mediaStatus == J.MediaStatus.Buffered) {
                 hide(false)
-                break;
+            } else if (manager.mediaStatus == J.MediaStatus.Buffering || manager.mediaStatus == J.MediaStatus.Stalled) {
+                show(false)
             }
         }
     }

sailfish/qml/harbour-sailfin.qml

@@ -131,11 +131,11 @@ ApplicationWindow {
 
     // Keep the sytem alive while playing media
     KeepAlive {
-        enabled: playbackManager.playbackState === MediaPlayer.PlayingState
+        enabled: playbackManager.playbackState == PlayerState.Playing
     }
 
     DisplayBlanking {
-        preventBlanking: playbackManager.playbackState === MediaPlayer.PlayingState
+        preventBlanking: playbackManager.playbackState == PlayerState.Playing
                          && playbackManager.hasVideo
                          && playbackManager.controllingSessionLocal // Must be controlling a local session
     }